Design, synthesis and antiviral evaluation of novel acyclic phosphonate nucleotide analogs with triazolo[4,5-b]pyridine, imidazo[4,5-b]pyridine and imidazo[4,5-b]pyridin-2(3H)-one systems

A new series of phosphonylated triazolo[4,5-b]pyridine (1-deaza-8-azapurine), imidazo[4,5-b]pyridine (1-deazapurine) and imidazo[4,5-b]pyridin-2(3H)-one (1-deazapurin-8-one) were synthesized from 2-chloro-3-nitropyridine and selected diethyl ɷ-aminoalkylphosphonates followed by reduction of the nitro group and cyclization. In the final step O,O-diethylphosphonates were transformed into the corresponding phosphonic acids. All synthesized compounds were evaluated in vitro for inhibitory activity against a broad variety of DNA and RNA viruses and their cytotoxic potencies were also established. Compound 12f showed marginal activity against cytomegalovirus Davis strain (EC50 = 76.47 μM) in human embryonic lung (HEL) cells while compounds 10g (EC50 = 52.53 μM) and 12l (EC50 = 61.70 μM) were minimally active against the varicella-zoster virus Oka strain in HEL cells. Compounds under investigation were not cytotoxic at the maximum concentration evaluated (100 µM).